(1) Field of the Invention
The present invention relates to improvements in a pump of the volumetric type for pumping compressible or non-compressible fluid.
(2) Description of the Prior Art
Japanese Unexamined Patent Publication No. 57-8385, published Jan. 16, 1982, discloses a novel volumetric pump of the so-called "oscillating ring" type which comprises a pumping member or "oscillating ring" driven by an eccentric drive along a circular oscillating trajectory within a pumping chamber. The pumping member comprises a hollow cylinder split along a longitudinal slot. The pumping chamber is defined by a cylindrical inner wall formed in a fixed plate and substantially encircled by the pumping member, a cylindrical outer wall formed in the fixed plate and substantially encircling the pumping member, a partition wall extending radially between the inner and outer walls through the slot in the pumping member, and a pair of opposite side walls in close contact with the sides of the pumping member, one of the side walls being formed on the fixed plate and the other on a movable plate carrying the pumping member and driven by the eccentric drive. The radial width of the pumping chamber is selected to be equal to the wall thickness of the pumping member plus the diameter of the circular trajectory of the eccentric drive, so that a substantial sealing contact is obtained between the inner wall of the pumping member and the inner wall of the pumping chamber, as well as between the outer wall of the pumping member and the outer wall of the pumping chamber during the oscillating movement of the pumping member.
However, this pump suffers from disadvantages in that at the top-dead-center(TDC) and bottom-dead-center(BDC) positions of the pumping member there is a considerable fluid leakage from the high pressure zone to the low pressure zone of the chamber due to the presence of gaps between the pumping member and the pumping chamber walls, as described later in more detail.